The Prophet ﷺ prayed Dhuhr, then mounted his riding camel, and when he reached the top of the hill of Bayda, he entered the state of ihram.
حدثنا أحمد بن حنبل حدثنا روح حدثنا أشعث عن الحسن
أن النبي ﷺ صلى الظهر ثم ركب راحلته فلما علا على جبل البيداء أهل
[Its chain is daif] Nasai narrated it in Manasik al-Hajj, chapter on Bayda, no. 2663, from the hadith of Ashath, and it is in Musnad Ahmad, 30/207. The hadith has corroborating narrations. Hasan Basri narrated it with "an" (without specifying direct hearing).